1. Field of the Invention
The present invention relates to a fuel injection quantity control device for limiting the fuel injection quantity so as to prevent the vehicle speed from exceeding the set limit vehicle speed.
2. Description of the Related Art
The maximum speed of trucks and tractors is sometimes limited due to legal restrictions or in order to reduce the noise or fuel consumption.
Such a vehicle speed limit control is conducted in such a manner that when the vehicle speed approaches the limit speed, the quantity of fuel injected into the engine is limited so that the vehicle speed does not exceed the limit vehicle speed.
More specifically, if the vehicle speed limit control is actuated, the difference between the actual acceleration value and target acceleration value is computed, a proportional term and an integral term are found from this difference, a basic fuel injection quantity for vehicle speed limit is determined by adding up those proportional term and integral term (see, for example, Japanese Patent Application Laid-open No. H10-250408), and the accelerator requested injection quantity is determined from the engine revolution speed and accelerator opening degree.
The basic fuel injection quantity for vehicle speed limit and accelerator requested injection quantity are compared to each other and the smaller of them is selected as the vehicle speed limit injection quantity that will be actually injected into the engine.
With the control device described in Japanese Patent Application Laid-open No. H10-250408, the vehicle speed is prevented from overshooting and exceeding the limit vehicle speed by finding the proportional term and integral term from the difference between the target acceleration value and actual acceleration value, rather than from the difference between the limit vehicle speed and actual vehicle speed, and determining the basic fuel injection quantity for vehicle speed limit from the proportional term and integral term.
However, the problem associated with the control device described in Japanese Patent Application Laid-open No. H10-250408 was that the fuel injection quantity corresponding to a gear position was not taken into account and overshoot could sometimes occur because the vehicle speed changes depending on the gear position, even if the injection quantity is the same.